Gas turbine engine blades are subject to various sources of excitation that may result in both natural modes and aero elastic responses. Engine testing and bench testing are used during gas turbine engine development testing to assess these modes and responses, as well as the amount of damping available to determine part stability. The engine testing and bench testing may operate the gas turbine engine at pressures and velocities that may induce blade flutter or other aero elastic phenomena that may negatively impact gas turbine engine performance.
The engine testing and bench testing may use shaker tables, airflow rigs, and strain gauged blades to study the dynamics and the actual operating environment. One form of excitation that is used in both engine testing and bench testing is the introduction of pulsed airstreams that emanate from probes positioned and timed to emit air pulses as the blades pass behind the probe. The timing and the accuracy of the delivery of the emitted air pulse is important to artificially excite the blades. The frequency of the emitted air pulse is limited due to the inertia and mechanical valves, or the speed at which the magnetically actuated valve can operate, or other limitations that may limit the frequency of the air pulses.
For example, blade flutter testing that uses a steady stream of air or fluid pulsations ejected from a set of probes ahead of a set of rotating blades has been done using electromagnetically controlled valves, but this system is limited in frequency to around 100 to 300 hz. However, there is a desire for air pulses that can be emitted at or above 1000 Hz. Further, there is a desire for air pulses that can be precisely timed to skew the pulses or advance and/or delay the pulses relative to other probes equally spaced around the blade set which requires extremely accurate timing and valve operation.
Accordingly, it is desirable to provide an improved way to provide air or fluid pulses to excite turbomachinery with superior timing.